Bipolar electrosurgical instruments apply radiofrequency energy to a surgical site to cut, ablate, or coagulate tissue. A particular application of these electrosurgical effects is to seal blood vessels or tissue edges. A typical instrument includes an end effector in the form of a pair of opposing jaws, with one or more electrodes on each jaw tip. In an electrosurgical procedure, the electrodes are placed in close proximity to each other as the jaws are closed on a target site such that the path of current between the two electrodes passes through tissue within the target site. The mechanical force exerted by the jaws and the electrical current combine to create the desired surgical effect. By controlling the level of mechanical pressure applied by the jaws, the gap distance between electrodes, and the intensity, frequency, and duration of the electrosurgical energy applied to the tissue, the surgeon can coagulate, cauterize, or seal tissue toward a therapeutic end.
Various approaches have been developed to control the delivery of energy during an electrosurgical procedure, including feedback to the output from a generator delivering energy to the electrodes, such as feedback based on the impedance in target tissue. The goal is to leave a high integrity seal surrounded by healthy tissue by applying no more and no less than the amount of energy required to create the desired effect within the targeted sealing site, while minimizing deleterious effects outside the target locale.
An anatomical variable that poses a challenge to the control and the efficacy of radiofrequency-based sealing relates to variation in the biochemical composition of target tissues. For example, one factor that may affect the success of electrosurgical sealing procedures relates to the relative collagen content of tissues. Tissues with a relatively high collagen content appear to be particularly amenable to effective sealing, while tissues with a relatively low collagen content (such as veins, muscle, kidney, spleen, lung, and liver) are relatively difficult to seal electrosurgically. Devices or methods that enhance the amenability of low collagen tissues to electrosurgical techniques could permit expansion of technology into these organ sites, and allow replacement of conventional methods of sealing, such as the use of staplers and sutures.